A turbine assembly, such as that used in power generation, typically generates rotating shaft power by expanding hot compressed gas produced by combustion of a fuel. Gas turbine buckets or blades generally have an airfoil shape designed to convert the thermal and kinetic energy of the flow path gases into mechanical rotation of the rotor.
The turbine buckets are frequently provided with tip shrouds. The tip shroud prevents failure of the airfoil in high cycle fatigue due to vibratory stresses. Further, a tip shroud seal typically projects radially outwardly from the outermost surface of the shroud, and extends circumferentially between opposite ends of the shroud in the direction of rotation of the turbine rotor. The tip shroud seal conventionally extends radially into a groove formed in a stationary shroud opposing the rotating tip shroud. In some designs, the stationary shroud has a honeycomb pathway. Rather than providing a zero tolerance seal between the tip shroud and the stationary shroud, resulting in instability of the airfoil, it has been found desirable to provide a leakage path over the tip shroud seal which will remove such instability. Typically, a cutter tooth is provided at the leading edge (also referred to as the suction side) of the tip shroud seal so as to cut a wider groove in the honeycomb pathway of the stationary shroud than the width of the tip shroud seal. This enables leakage flow between the high and low pressure regions on opposite sides of the tip shroud seal within the groove. While this results in an undesirable decrease in pressure drop across the airfoil with resulting diminishment of sealing capability, the lost efficiency is compensated by an increase in the stability of the airfoil.
Tip shrouds, however, are subject to creep damage due to the combination of high temperatures and centrifugally induce bending stresses. The failure of a single bucket or blade may cause the entire turbine to be taken offline. In addition to the downtime, such a repair of a bucket is time consuming and/or expensive. There is a desire, therefore, for a turbine blade shroud with improved ability to handle temperature and stress. Such a turbine blade shroud should provide increased lifetime while also increasing the efficiency of the turbine system as whole.